Quantum mechanics, its properties including wavefunctions, complex numbers and uncertainty, are necessary and completely reasonable and understandable, with no weirdness. Classical physics is impossible. Much uncertainty comes from Fourier analysis. Waves and particles and collapse of wavefunctions are meaningless. Their seeming appearance in analyzed. Reasons and limitations of superposition are considered. Gravitation is an example of nonlinearity. All objects interact so nonlinearity is universal. How quantum mechanics then fits in is shown. Dirac's equation comes from Poincaré group. Physics is necessarily impossible in any space but that with dimension 3+1. Spin-statistics is a property of rotation groups.